1. Field of the Invention
This invention relates to a video data communication system and method in which video data is transmitted between devices connected to a data bus according to a protocol which ensures the security of the transmitted video data.
2. Description of the Related Art
Video data devices are connected to a common data bus to facilitate the communication of video data among the devices. Such devices include video signal receivers, video signal decoders, video signal recorders, video signal processing devices, video signal display devices, and video signal reproducing or playback devices. The data bus architecture has the advantage of being easy to implement, modify, and expand.
A video data bus system which conveys digital video data signals has the added advantage of substantially preserving the integrity of digital video signals transmitted on the bus. Such a system may transmit video data at great speeds without degrading the quality of the transmitted signal. Such a system is particularly useful for reproducing and disseminating copyrighted video data.
To preserve the value of copyrighted video data, a data bus communication system is needed that can selectively prevent certain devices connected to the bus from accessing certain video data but allowing such devices to access other video data. Also, a flexible communication protocol is needed to facilitate the secure and organized flow of video data through a video data bus system.
An object of the present invention is to provide a communication system in which the security of video data transmitted on a data bus is maintained.
Another object of the present invention is to prevent the unauthorized retrieval, reproduction, or display of video data transmitted on a video data bus.
Yet another object of the present invention is to provide a method for securely communicating video data among particular devices connected to a common video data bus.
A further object of the invention is to provide a communication system in which a device connected to a common data bus is able to address particular other devices for the transfer of video data thereamong.
A still further object of the invention is to provide a communication system in which devices connected to a common data bus can issue control signals to other devices to initiate specific types of video data transfers.
Another object of the present invention is to provide a communication system in which video data signals are transmitted on a video data bus without specifically included address signals.
In accordance with one aspect of the present invention, a method for communicating video data via a data bus between a master device and a slave device which are each coupled to the bus, comprises the steps of transmitting a slave address of the slave device and a command from the said master device to said data bus, generating, at said master device, a KEYCMD signal as a function of said command and a master security key, receiving, at said slave device from said data bus, said slave address and said command and recognizing said slave address as corresponding to said slave device, generating, at said slave device, an ACK signal as a function of said command and a slave security key, transmitting from said slave device to said data bus a master address of said master device and said ACK signal, receiving, at said master device from said data bus, said master address and said ACK signal and recognizing said master address as corresponding to said master device, comparing said KEYCMD signal generated by said master device with said ACK signal received by said master device, and executing a data transfer between said master device and said slave device if said KEYCMD signal corresponds to said ACK signal.
In accordance with another aspect of the present invention, in a system for communicating video data between at least one master device having a master address and at least one slave device having a slave address by way of a data bus coupled to said master device and to said slave device; said master device includes means for transmitting to said data bus said slave address and a command, means for generating a KEYCMD signal as a function of said command and a master security key, means for receiving from said data bus said master address, and an ACK signal, means for recognizing said master address as corresponding to said master device, means for comparing said KEYCMD signal and said ACK signal, and means for receiving said video data from said data bus if said KEYCMD signal corresponds to said ACK signal; and said slave device includes means for receiving from said data bus said slave address and said command, means for recognizing said slave address as corresponding to said slave device, means for generating said ACK signal as a function of said command and a slave security key, and means for transmitting to said data bus said master address, said ACK signal, and said video data.
In accordance with still another aspect of this invention, in a system for communicating video data between at least one master device having a master address and at least one slave device having a slave address by way of a data bus coupled to said master device and to said slave device; and said master device includes means for transmitting to said data bus said slave address and a command, means for generating a KEYCMD signal as a function of said command and a master security key, means for receiving from said data bus said master address and an ACK signal, means for recognizing said master address as corresponding to said master device, means for comparing said KEYCMD signal and said ACK signal, and means for transmitting to said data bus said video data if said KEYCMD signal corresponds to said ACK signal; and said slave device includes means for receiving from said data bus said slave address, said command and said video data, means for recognizing said slave address as corresponding to said slave device, means for generating said ACK signal as a function of said command and a slave security key, and means for transmitting to said data bus said master address and said ACK signal.
In accordance with a feature of this invention, in executing a data transfer, the data in said master device is encrypted according to an encryption key and the data in said slave device is decrypted according to said encryption key, and said slave address and said encryption key are transmitted from said master device to said data bus and said encryption key and said slave address are received at said slave device from said data bus with said slave address being recognized as corresponding to said slave device. Alternatively, in executing a data transfer, the data in said slave device is encrypted according to an encryption key and said data in said master device is decrypted according to said encryption key, said master address and said encryption key are transmitted from said slave device to said data bus and said mater address and said encryption key are received from said data bus at said master device with said master address being recognized as corresponding to said master device.
The above, and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings in which the same components are identified by the same reference numerals.